The former Oceanside High football star had gone on to become the most dominant linebacker of his era with the San Diego Chargers. He retired from football in 2009.

His death Wednesday stunned the San Diego sports and local education community.

"My first reaction was 'Why?'" said Willie Buchanon, a 1968 graduate of Oceanside High who played in the NFL from 1972-82. "We lost an Oceanside Pirate, a San Diego Charger. He was on top of the world. To take his life like this, we don't know what led him to this.

Seau was selected by the Chargers in the first round of the 1990 NFL draft with the fifth overall pick.

He went on to become a 12-time Pro Bowl selection and a six-time first-team All-Pro. He also helped the Chargers reach their only Super Bowl in 1995.

"I can't put into words how I'm feeling right now," Chargers President Dean Spanos said in a statement. "I'm shocked and devastated."

Seau played for three NFL teams, the Chargers, Miami Dolphins and the New England Patriots, from 1990-2009. He had 56 1/2 sacks and 18 interceptions during his career.

In his hometown of Oceanside, Seau was revered. He graduated in 1987 from Oceanside High School, where he starred in football and basketball.

"Without question, he was the greatest athlete ever to come out of North County, and one of the three best to come out of San Diego, with Bill Walton and Marcus Allen being the others," said Steve Scholfield, who covered Seau during his high school and pro career while working for the Blade-Citizen and later as the longtime sports editor and columnist for the North County Times.

Seau remained close to Oceanside long after graduating from high school. He started a foundation in 1992 that gave scholarships to local students and raised money and resources to help children face problems related to child abuse and drugs.

He had a powerful effect on local high school students, through philanthropy as well as inspiration, officials said Wednesday.

Jessica Poumele, who went to school with him and now is a curriculum coordinator at Oceanside High, said he will be sorely missed.

"He has motivated and inspired our students here that they can really accomplish anything that they set their mind to," Poumele said. "It's just such a loss for this community and the school."

Family members plan to honor Seau as part of a celebration of Polynesian culture that was already planned for Friday at Oceanside High, said Sili So'oto, Seau's cousin.

"He was our local hero," she said. "You cannot mention Junior Seau and not get a smile on your face."

Seau inspired So'oto's son, Vic, to become a football player. He signed to play with the Green Bay Packers last year.

Oceanside High officials planned to send a message to students and parents Wednesday afternoon, letting them know about Seau's death.

Counselors are on standby for any students or educators who need them, Hurst said.

In September, Seau donated $25,000 to Oceanside High to build an athletic obstacle course for students there.

He said at the time that he was excited to be able to help his alma mater.

"Allowing us to have (the course) in my high school, in my hometown, is a great honor," he said at the time.

Every student on the campus has used the course as part of physical education classes, Hurst said.

Dana Martin, public relations coordinator for the Oceanside Boys & Girls Club, said the organization had received numerous donations from Seau over the years.

She said the Junior Seau Fitness Center was opened to the public Wednesday so that community members could get together to mourn Seau.

"Junior was obviously a great impact on our club. He contributed so much to where we are today," Martin said. "He really inspired a lot of kids and touched their lives. He showed them that they could grow up in this neighborhood and be a success like he was."

As a child, Seau attended Laurel Elementary and Jefferson Junior High in Oceanside. He was inducted into Laurel's Hall of Fame in 2001 and into Oceanside High's in 2010.